1. Field of the Invention
The present invention relates to a content sales period verifying system and a content decryption key effective period verifying system in a content sales system for selling contents on line.
2. Description of the Related Art
With a widespread use of CD-ROM drives, a content such as a film, musical work, computer program, database, etc., in the form of software and defined as digital data is frequently distributed through a CD-ROM medium. The CD-ROM medium can be manufactured at low costs and has a large capacity exceeding 500 MB. In addition, CD-ROM drives are decreasing in price and increasing in speed. Further, the CD-ROM is comparatively lightweight and thin for its storage capacity and, therefore, can be distributed by various methods, including being interposed in a magazine for distribution or other uses.
The content of the CD-ROM is stored as digital data, therefore the content can be illegally copied and installed (the term “install” herein connotes an introduction of the content into a disk device of a personal computer). Accordingly, when distributing the content of the CD-ROM, illegal copying and installation must be prevented.
Accordingly, the following has hitherto been practiced to date. In distributing the content by CD-ROM, several types of trial version contents and an encrypted real content are recorded on the CD-ROM, and thus distributed. Only a user paying a using charge (which is a one-time payment) for the content is supplied with a key for decrypting the encrypted real content, permitting the user to use the real content. For the purpose of explanation, the phrase “supplying the key in exchange of the payment of the using charge for the content” is expressed such as “selling the content”.
By the way, in the traditional over-the-counter selling of the contents, there must be several cases where the contents are sold with a predetermined limit of a sales period as in the case of weekly and monthly magazines or seasoning goods, where the sales of unpopular contents are discontinued, and where the sales of old versions are terminated due to a version-up of the computer program. It is therefore desired that the content sales system should meet those cases even when selling the contents in the form of the digital data. Namely, it is desirable to construct a novel content sales system capable of previously setting a sales period for which the contents can be sold and newly setting or shortening a sales period depending on circumstances after a start of sales.
The conventional content sale system employing the CD-ROM is, however, not able to meet the cases described herein above.